[stgt] [PATCH v3] tgtd: refresh ready fds of event loop after event deletion

[Hitoshi Mitake]

At Wed, 26 Feb 2014 14:22:21 +0900,
FUJITA Tomonori wrote:
> 
> On Wed, 26 Feb 2014 14:13:22 +0900
> Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp> wrote:
> 
> > Current main event loop (event_loop()) of tgtd has a possibility of
> > segmentation fault. The problem is caused by the below sequence:
> > 
> > 1. Event A, B are ready so epoll_wait(2) returns.
> > 2. The handler of the event A is called. In the event handler, the
> >    event B is deleted with tgt_event_del()
> > 3. event_loop() tries to call the handler of the event B. It causes
> >    segfault because the event struct is already removed and freed.
> > 
> > For avoid this problem, this patch adds a new global variable
> > event_need_refresh. If the value of this variable is 1, event_loop()
> > calls epoll_wait(2) again for refreshing ready fd list. This patch
> > also lets tgt_event_del() to turn on the flag in its tail.
> > 
> > For example, we can produce segfault of tgtd under heavy load. Below
> > is a backtrace obtained from the core file:
> >  (gdb) bt
> >  #0  0x0000000000000000 in ?? ()
> >  #1  0x0000000000411419 in event_loop () at tgtd.c:414
> >  #2  0x0000000000411b65 in main (argc=<value optimized out>, argv=<value optimized out>) at tgtd.c:591
> > 
> > To be honest, I still don't find an event handler which calls
> > tgt_event_del() for other fds. But with this modification, the above
> > segfault is avoided. The change seems to be effective.
> 
> As you pointed out off-line, making a connection closed via tgtadm
> might be the case. Anyway, I think that the handler API should allow
> removing other handlers from a handler. Merged, thanks a lot!
> 
> > +int event_need_refresh;
> > +
> 
> static?

Ah, the variable should be static one. I'll send a patch later.

Thanks,
Hitoshi
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